1. Field of the Invention
The present invention relates to a mold assembly for making an ocular device such as a contact lens, an intraocular lens or a blank which is later lathed to make a lens.
2. Description of the Related Art
Certain mold assemblies for making ocular devices such as contact lenses, intraocular lenses or lens blanks consist of two pieces that include a male mold segment and a female mold segment. Typically, such assemblies include frustoconical or tapered walls on one of the segments to align the segments as the latter are brought together during a molding operation. Examples of two-piece mold assemblies are described in U.S. Pat. Nos. 4,121,896 and 4,197,266.
Other types of mold assemblies for making ocular devices consist of three pieces which include a sleeve and two segments that fit within the sleeve. Examples of three-piece mold assemblies are described in U.S. Pat. Nos. 3,761,208, 4,166,088 and 4,836,960.
However, the quality of a molded ocular lens is dependent upon the mold assembly that is used to make the lens. A mold assembly that is dimensionally accurate and stable during use facilitates the manufacture of a dimensionally accurate and thus optically correct lens.
A precision mold assembly may be made from metallic materials which can be machined to precise tolerances. It has also been proposed to reduce the cost of lens assemblies by making the assemblies of plastic materials which can be injection molded. However, typical plastic lens mold assemblies are less rigid than corresponding assemblies made of metallic materials and may cause the finished lens to assume an incorrect contour or dimension.
In some instances, it is desirable to use a mold assembly that has a tracking segment which moves during curing of the molding material to maintain contact with the latter as the material expands or contracts. Often, a flexible gasket or rim is placed between the segments in an attempt to contain the liquid lens molding material within the mold cavity during tracking, while also forming the edge of the molded lens. However, it is sometimes difficult to ensure that the gasket or rim has sufficient flexibility to permit free, unhindered tracking, while still maintaining a proper pinch-off and seal in order to contain the mold material within the liquid cavity.